**Question:** A farmer rearing sheep is presenting with fever and weakness for the last one month, along with generalised lymphadenopathy and hepatomegaly. Liver biopsy shows non-caseating granuloma. These are most likely due to infection with -

A. Tuberculosis
B. Leishmaniasis
C. Q fever
D. Brucellosis

**Correct Answer:** D. Brucellosis

**Core Concept:**
Brucellosis is a zoonotic infection caused by the bacterium Brucella species, primarily affecting ruminants like sheep and cattle. In humans, it can present with a spectrum of clinical manifestations, including fever, weakness, and lymphadenopathy. Non-caseating granulomas in liver biopsies are a characteristic feature of brucellosis.

**Why the Correct Answer is Right:**
Non-caseating granulomas in liver biopsies are seen in brucellosis, as well as in tuberculosis and Q fever. However, the key differentiating factor for Brucellosis is the presence of fever and weakness, which are not usually prominent in tuberculosis or Q fever. Additionally, brucellosis is more likely to cause hepatomegaly. Leishmaniasis typically presents with skin lesions and visceral involvement, not the combination of fever and lymphadenopathy.

**Why Each Wrong Option is Incorrect:**
A) Tuberculosis: While tuberculosis can cause granulomas, the fever and weakness are usually more severe in brucellosis. Leishmaniasis typically presents with skin lesions and visceral involvement, not fever and lymphadenopathy.
B) Leishmaniasis: Leishmaniasis usually presents with cutaneous lesions and visceral involvement, not fever and lymphadenopathy.
C) Q fever: Q fever typically presents with fever and hepatosplenomegaly, not the combination of fever and lymphadenopathy. Fever and weakness in Q fever are usually milder than in brucellosis.
D) Brucella melitensis: Brucella species are responsible for causing brucellosis, which presents with fever, weakness, and lymphadenopathy. The combination of these symptoms along with hepatomegaly makes Brucella melitensis the correct answer.

**Clinical Pearl:**
Brucellosis is a zoonotic infection caused by bacteria from the Brucella genus, typically transmitted through consumption of unpasteurized dairy products or contact with infected animals. Clinical manifestations include fever, weakness, and lymphadenopathy, especially in the abdominal region. Additionally, hepatomegaly is often seen in brucellosis. This differential diagnosis is important as prompt diagnosis and treatment can prevent severe complications and improve patient outcomes.